Mechanical properties of HFCVD microcrystaline diamond coated on seeded WC substrate

Abstract

The mechanical properties and adhesion strength of a diamond film coated on cemented carbide has great significance in its performance as a cutting tool. Many studies have been conducted to improve the mechanical properties through the careful optimization of a variety of substrate pretreatment techniques. In this study, a two step chemically pretreated WC-6% Co was seeded with a solution of diamond powders (0.5µm) having fixed concentration (0.8 g/l) mixed with varying SiC powders (175µm) concentration of 1.0, 5.0 and 10.0 g/l respectively so as to produce different microcrystalline diamond film surface roughness. Diamond films were grown on the pretreated tungsten carbide (WC) substrates using hot filament chemical vapour deposition (HFCVD) technique for 30 hours with fixed parameter. Field emission scanning electron microscope (FESEM) images and x-ray diffraction (XRD) spectrums results indicates that all the diamond films have well faceted grains of (111) and (220) morphologies. The WC substrates etched and seeded with 1g/l of SiC mixed with 0.8g/l of diamond powders was found to have diamond coating with sharp peaks with uniform height and gaps between diamond grains when observed using atomic force microscope (AFM). Sand blasting technique was employed to determine the adhesion strength of the coated diamond film, where the sample seeded with a mixture of diamond with 5 g/l SiC powder concentration was found to have the highest diamond film adhesion strength. Nano-scratch tests show that all the diamond films have excellent adhesion with the mode of deformation found to be cohesive chipping rather than adhesive failure. Nano-indentation tests using Berkovich indenter revealed that the substrate seeded with diamond mixed with 5 g/l concentration of SiC powders was found highest in hardness (104.3 GPa) and modulus(1115 GPa) which is comparable to natural diamond properties.